Add support for ARM64 builds

This change adds support for building PVE Edge kernel on ARM64. See #363
for more information.

debian/rules.d/arch/arm64.mk

@@ -0,0 +1,5 @@
+KERNEL_BUILD_ARCH	= arm64
+KERNEL_HEADER_ARCH	= $(KERNEL_BUILD_ARCH)
+KERNEL_BUILD_IMAGE	= Image
+KERNEL_IMAGE_PATH	= arch/$(KERNEL_BUILD_ARCH)/boot/${KERNEL_BUILD_IMAGE}
+KERNEL_INSTALL_FILE	= vmlinuz